# How rapidly can a commercial aircraft descend? **URL:** \ **Category:** Factual Questions\ **Created:** [January 25, 2011, 4:34pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932 "2011-01-25T16:34:15Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 25, 2011, 4:34pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/1 "2011-01-25T16:34:15Z")
News today reported that [a commercial airliner performed an emergency descent](http://www.msnbc.msn.com/id/41252759/ns/travel-news/) after losing cabin pressure. The [oxygen generators](http://en.wikipedia.org/wiki/Oxygen_generator#Chemical_oxygen_generator_in_commercial_airliners) that provide passengers with emergency O[sub]2[/sub] reportedly last for 15-20 minutes after ignition, so I guess they’ve got that big a window in which to descend to a safe altitude, but how rapidly _can_ they make the descent? Moreover, how do the configure for the descent: -shallow descent path at high airspeed, with moderate drag (spoilers partially deployed), or -very steep descent at low airspeed, with high drag (full spoilers, flaps, gear-down)? In the former, a moderate-drag config would hold airspeed steady at a high-value, but in a shallow dive; the latter is a steeper dive, but the high-drag config should hold airspeed to a lower value. So which strategy provides the greatest _vertical_ speed, and what other considerations come into play in deciding on how to get from cruise altitude to an altitude where supplemental O[sub]2[/sub] isn’t needed? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 25, 2011, 4:44pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/2 "2011-01-25T16:44:47Z")
It seems the answer is, “it depends”. Depends what is wrong with your plane requiring an emergency descent. IANAPilot but I found this which seems to be from a 747 pilot: > [@](#): > > The subject you friends talk about is separated in two procedures for pilots. > xxx > “Loss of pressurization” is the first one. It can be gradual, forcing the crew to descend to a lower altitude, or it can be explosive decompression, forcing an emergency descent… > xxx > “Emergency descent” is the second procedure to mention. It can be performed two different ways - if you have structural integrity of the plane, that is often the case for a mere loss of pressurization, or if you had an explosive decompression (maybe a cargo door blew open, tearing a part of the structure of the fuselage). > xxx > Loss of pressurization, first thing to do is get on oxygen masks, establish communications, see if cabin pressure loss can be compensated by adding sources of bleed air, or extra air conditioning pack… close the outflow valves. > If it does not work, descend to a lower altitude… > xxx > Emergency descend (Boeing 707, 727 or 747 described here) can be done two different ways. Depends if you have structural integrity or not. One method is to descend immediately with spoilers, at Mmo/Vmo, this will bring you “down” faster initially, but you will reach a safe altitude later. The other slows down the aircraft to gear extension speed (Mach .82/270 KIAS) with the spoilers, then extend the gear, then start your descent and accelerate to gear extended speed (Mach .82/320 KIAS). This initially delays your descent, but you will reach your safe altitude earlier. > xxx > I prefer the first method, gear up, descend with the spoilers only, gear remains up, at Mmo/Vmo, and I will use the autopilot at least initially, 5,000 fpm. In this procedure, the passengers are less likely to panick, because the angle of descent will not be as steep, and the gear up will reduce noise. If I initiate an emergency descent, I bank the airplane a lot to start the descent, that is 45 to 60 degrees bank, that is not to give negative “Gs” to the passengers and send them against the ceiling of the cabin. > > SOURCE: [Airliners.net - Aviation Forums](http://www.airliners.net/aviation-forums/tech_ops/read.main/82291/) ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [January 25, 2011, 4:50pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/3 "2011-01-25T16:50:34Z")
> [@Machine\_Elf](#): > > -shallow descent path at high airspeed, with moderate drag (spoilers partially deployed), or > > -very steep descent at low airspeed, with high drag (full spoilers, flaps, gear-down)? not a real answer, but flaps and gear can’t be deployed above a certain airspeed - the stress as a result would be a not good thing. you have to be going pretty damn slow to operate with full flaps, which seems at odds with a very steep descent. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [January 25, 2011, 4:57pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/4 "2011-01-25T16:57:26Z")
Not a pilot, but I was on a plane once from Providence, RI to Houston. Midway through the flight, they made an announcement asking if a physician was on board. One was, and he determined that a passenger was suffering from a heart attack, and needed to get to a hospital immediately. The pilot came on and told us that we were diverting to Nashville, TN. He then appeared to point the plane to the ground. It was the fastest descent I’ve ever experienced. From the time the pilot made the announcement (presumably at cruising altitude) to the time we landed was about 10 minutes. As we sped down the runway after landing, we could see ambulance lights racing toward the plane. These two guys rushed on who looked like they were ready for anything. They had latex gloves and masks on, had all kinds of medical gear strapped on, not to mention holstered pistols. They had the guy off the plane in less than a minute and into the ambulance. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 25, 2011, 6:09pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/5 "2011-01-25T18:09:57Z")
I knew a guy who flew 747s for 10+ years and said (IIRC) that in an emergency they were capable of descending at 10,000 ft/min (close to 100 knots). ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [January 25, 2011, 7:30pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/6 "2011-01-25T19:30:27Z")
32 feet per second per second. 😃 ---
**Author:** ![Mr.Excellent](https://avatars.discourse-cdn.com/v4/letter/m/f19dbf/32.png) [@Mr.Excellent](https://boards.straightdope.com/u/Mr.Excellent)\ **Post date:** [January 25, 2011, 7:39pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/7 "2011-01-25T19:39:27Z")
> [@runner pat](#): > > 32 feet per second per second. 😃 Or 9.8 meters per second per second. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [January 25, 2011, 7:59pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/8 "2011-01-25T19:59:00Z")
> [@robby](#): > > not to mention holstered pistols. Firearms or some medical device that resembles a pistol? ---
**Author:** ![Suburban\_Plankton](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suburban_plankton/32/219_2.png) [@Suburban\_Plankton](https://boards.straightdope.com/u/Suburban_Plankton)\ **Post date:** [January 25, 2011, 8:02pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/9 "2011-01-25T20:02:51Z")
No one is certain, but it’s thought that a China Airlines 747 might have gone supersonic during an emergency descent in 1985. According to the [Wikipedia article](http://en.wikipedia.org/wiki/China_Airlines_Flight_006), “Altitude decreased 10,000 ft (3,000 m) within only twenty seconds.” and “They had descended 30,000 ft (9,100 m) in under two and a half minutes”. That’s a bit faster of a descent than \*\*Xema \*\*cites, but it was also not exactly ‘controlled’. It does give you a bit of respect for the designers at Boeing, though… ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [January 25, 2011, 8:06pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/10 "2011-01-25T20:06:39Z")
> [@carnivorousplant](#): > > Firearms or some medical device that resembles a pistol? No, they appeared to be firearms. They also had police badges. I guess they were a combination of paramedic and police, which is something that I’ve never seen before. I remember that they had pistols in holsters on one hip, and big pairs of medical scissors on the other hip. They also had handcuffs. ---
**Author:** ![Suburban\_Plankton](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suburban_plankton/32/219_2.png) [@Suburban\_Plankton](https://boards.straightdope.com/u/Suburban_Plankton)\ **Post date:** [January 25, 2011, 8:26pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/11 "2011-01-25T20:26:29Z")
> [@Suburban\_Plankton](#): > > No one is certain, but it’s thought that a China Airlines 747 might have gone supersonic during an emergency descent in 1985. According to the [Wikipedia article](http://en.wikipedia.org/wiki/China_Airlines_Flight_006), “Altitude decreased 10,000 ft (3,000 m) within only twenty seconds.” and “They had descended 30,000 ft (9,100 m) in under two and a half minutes”. > > That’s a bit faster of a descent than \*\*Xema \*\*cites, but it was also not exactly ‘controlled’. It does give you a bit of respect for the designers at Boeing, though.. From the [NTSB report on the incident](http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/ComAndRep/ChinaAir/AAR8603.html): “The examination of the DFDR readout disclosed a number of periods where data were lost. These data losses were the result of the vibration and the sustained vertical acceleration forces (Gs) exerted on the recorder during the descent. Some of these data were retrieved through the use of recovery techniques, but the accuracy of these recovered data is suspect. In addition, anomalies in the recorded altitude and airspeed values appeared early in the descent because the descent rate of the airplane had exceeded the maximum tracking capability of the airplane’s digital air data computer (DADC). Specific details are discussed below.” “Between 1015:23 and 1017:15, the airplane descended from 30,132 feet to 9,577 feet. During this period, except for some short 3- to 7-second intervals of accurate data, the data recorded by the DFDR were, as stated earlier, either unreliable or erroneous.” “The maximum vertical acceleration forces recorded during the descent were 4.8Gs and 5.lGs as the airplane descended through 30,552 feet and 19,083 feet, respectively. The 5.1G peak value was recorded on a portion of the tape where data had been lost originally and subsequently recovered, but this value is consistent with the adjacent data which show an arresting of descent rate and a pull-up.” There were two “serious” injuries among the 274 people on board. I’d say this is probably provides an “upper limit” to the answer of “how rapidly \*can \*they make the descent?” , for aircraft in service today. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [January 25, 2011, 8:30pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/12 "2011-01-25T20:30:34Z")
> [@robby](#): > > No, they appeared to be firearms. They also had police badges. I guess they were a combination of paramedic and police, which is something that I’ve never seen before. > > I remember that they had pistols in holsters on one hip, and big pairs of medical scissors on the other hip. They also had handcuffs. Perfect occupation for a new TV drama: Paramedic Cops of Nashville. ---
**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\ **Post date:** [January 25, 2011, 8:34pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/13 "2011-01-25T20:34:21Z")
> [@runner pat](#): > > 32 feet per second per second. 😃 Plus the thrust of the engines. Easily supersonic until the airframe failed. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 25, 2011, 8:35pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/14 "2011-01-25T20:35:42Z")
> [@Rumor\_Watkins](#): > > not a real answer, but flaps and gear can’t be deployed above a certain airspeed - the stress as a result would be a not good thing. > > you have to be going pretty damn slow to operate with full flaps, which seems at odds with a very steep descent. on a 3-degree descent path (e.g. on final), my understanding is that full flaps and gear-down requires a significant application of power to maintain ~160-170 knots. I would think that idling the engines and adding in full spoiler would allow a considerably steeper descent path without exceeding the flaps-down speed limit. The question is whether the vertical speed in this case would be greater than the vertical speed for some other configuration with a higher forward speed, e.g. spoilers-only or spoilers w/gear-down. If **Whack-a-Mole’s** cite is accurate, then it appears spoilers w/gear-down is the fastest way to descend from cruise altitude to an altitude safe for an unpressurized cabin. ---
**Author:** ![JoelUpchurch](https://avatars.discourse-cdn.com/v4/letter/j/f05b48/32.png) [@JoelUpchurch](https://boards.straightdope.com/u/JoelUpchurch)\ **Post date:** [January 25, 2011, 11:28pm UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/15 "2011-01-25T23:28:52Z")
> [@robby](#): > > As we sped down the runway after landing, we could see ambulance lights racing toward the plane. These two guys rushed on who looked like they were ready for anything. They had latex gloves and masks on, had all kinds of medical gear strapped on, not to mention holstered pistols. They had the guy off the plane in less than a minute and into the ambulance. Sounds to me like one of the scenarios they deal with is hijackers faking a medical emergency. ---
**Author:** ![Shmendrik](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shmendrik](https://boards.straightdope.com/u/Shmendrik)\ **Post date:** [January 26, 2011, 12:20am UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/16 "2011-01-26T00:20:28Z")
> [@JoelUpchurch](#): > > Sounds to me like one of the scenarios they deal with is hijackers faking a medical emergency. Or they carry them in case of an equine medical emergency. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [January 26, 2011, 1:14am UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/17 "2011-01-26T01:14:44Z")
Took a plane into Burbank airport in CA. For noise abatement purposes they needed a steep descent, flaps out, gear down. The plane shook like a paint mixer as we headed down. Several passengers were horrified, and I wasn’t thrilled either. Sitting next to me was a pilot hopping a free ride, chugging beers from a cooler he carried on. He said not to worry about it, perfectly safe, but he’d downed at least 10 cold ones already. The plane pulled up to a shallow descent rapidly and landed smoothly. I prefer other airports. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 26, 2011, 2:04am UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/18 "2011-01-26T02:04:59Z")
I checked with another airline pilot friend - who now flies for Citation Shares. He said the 747 is a bit too clean and heavy for outstanding performance in this competition. Heavy, the best it can safely do is not much more than 6000 fpm; lightly loaded, 8000+. The champion is apparently the DC-8, whose thrust reversers can be activated in flight (not true for any Boeing he’s flown). He didn’t know the exact figure, but guessed it could easily be 12000+. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [January 26, 2011, 2:14am UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/19 "2011-01-26T02:14:50Z")
> [@Xema](#): > > The champion is apparently the DC-8, whose thrust reversers can be activated in flight Holy shit. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [January 26, 2011, 2:24am UTC](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932/20 "2011-01-26T02:24:57Z")
> [@Machine\_Elf](#): > > News today reported that [a commercial airliner performed an emergency descent](http://www.msnbc.msn.com/id/41252759/ns/travel-news/) after losing cabin pressure. A [second QANTAS jet in less than 24 hours](http://www.news.com.au/travel/news/another-engine-problem-for-qantas/story-e6frfq80-1225994833407) has had an inflight incident. The 747 returned to its origin only 30 minutes into the flight because of engine problems. They did not want to descend too quickly, either. [Next page](https://boards.straightdope.com/t/how-rapidly-can-a-commercial-aircraft-descend/568932.md?page=2)